The present invention relates to an r.f. power amplifier comprising a switching device and a load network capable of adjusting the relative phase of the voltages across and currents through the switching device.
One known amplifier of this type is the so-called "Class E" amplifier described, for example, in U.S. Pat. No. 3,919,656. This amplifier comprises a switching device, such as a transistor with a parasitic capacitance, and a reactive load circuit which adjusts the phase of the voltages and currents to obtain high efficiency. Due to the Q of the load circuit, the peak voltage swing across the switching device is often much larger than the power supply voltage. This means that the switching device has to have a large breakdown voltage as well as other parameters required for high efficiency such as a low on-resistance. These parameters give rise to conflicting design rules when designing the switching device.
An object of the present invention is to enable these design rules to be relaxed.